Microbial fuel cells are known from the prior art. For example, WO 2007/006107 discloses a microbial fuel cell that comprises a reactor, and each reactor comprises an anode compartment, a cathode compartment and a membrane, where the membrane separates the anode compartment and the cathode compartment from each other. The anode compartment contains micro-organisms capable of oxidizing organic electron donor compounds, the electrons being supplied to the anode in the anode compartment. According to WO 2007/006107, the organic electron donor compound in question can be glucose, sucrose, an acetate or a reducing compound of the type occurring for example in domestic sewage and the effluent of bio-refineries.
Other microbial fuel cells are described for example in: Logan et al., 2006, Lovley, 2006a; Lovley, 2006b; Rabaey and Verstraete, 2005, and Verstraete and Rabaey, 2006. The oxidation of the electron donor compounds can be catalysed for example by anodophilic and/or cathodophilic micro-organisms and redox enzymes. In some applications, hydrogen is produced in the cathode compartment as an energy carrier, instead of electricity (Liu et al., 2005; Rozendal et al., 2006).
Some fuel cells are designed in such a way that it is possible to transform photosynthetic activities into electricity. U.S. Pat. No. 3,477,879 discloses a device for converting light energy into electrical energy, where the device consists of an anode compartment containing an aqueous medium, where this aqueous medium contains live and dead algae and minerals, including sulphide, that occur in sea water, and a cathode compartment containing an aqueous medium, where this aqueous medium contains bacteria and minerals, including sulphate, that occur in sea water. The anode compartment and the cathode compartment are connected by an ion bridge or “salt bridge”. The live algae are capable of producing oxygen. When the device is in operation, dead algae are pumped from the anode compartment into the cathode compartment, where they serve as a nutrient for the bacteria that are capable of converting sulphate into sulphide. When sulphate is converted into sulphide, electrons are taken up. Sulphide is converted into sulphate and hydrogen ions (H+) at the cathode, as a result of which electrons are released at the cathode which are taken up again by oxygen via the anode, and the oxygen is then converted into hydroxide ions (OH−). The hydrogen ions and the hydroxide ions diffuse across the salt bridge and combine to form water, which completes the electrical circuit.
U.S. Pat. No. 4,117,202 and CA 1,099,332 disclose a biological electrical cell, where use is made of isolated mesophilic cells derived from what are called C4 plants, i.e. plants capable of converting CO2 into organic compounds containing four carbon atoms, for example oxalacetate, aspartate and malate. Such cells are also described in Rosenbaum et al., 2005a and Rosenbaum et al., 2005b. Isolated C4 photosynthesizing plant cells, green algae or (hydrogen producing) bacteria are used in these devices.
A disadvantage of the microbial fuel cells according to WO 2007/006107 is that an effluent stream such as domestic waste water is used. Effluent streams are not sustainable or renewable, and cannot be sustainably obtained, due to transport, for example. A great deal of energy is invested before effluent streams are obtained, and this involves a large CO2 emission from fuels, for example fossil fuels or radioactive waste released in the generation of nuclear energy. It is true that by increasing the production of effluent streams, more energy can be produced by fuel cells, but such a method does not offer a sustainable or renewable solution for the increasing world consumption of electrical energy. It is therefore better to generate or regenerate energy in a sustainable or renewable way. The present invention provides a solution for the problem of reducing non-sustainable and non-renewable energy.